Abstract

V 6O 13 is a promising Li-ion battery cathode material for use in the high temperature oil field environment. The material exhibits a high capacity, and the voltage profile contains several plateaus associated with a series of complex structural transformations, which are not fully understood. The underlying mechanisms are central to understanding and improving the performance of V 6O 13-based rechargeable batteries. In this study, we present in situ X-ray diffraction data that highlight an asymmetric six-step discharge and five step charge process, due to a phase that is only formed on discharge. The LixV 6O 13 unit cell expands sequentially in c, b, and a directions during discharge and reversibly contracts back during charge. The process is associated with change of Li ion positions as well as charge ordering in LixV 6O 13. Density functional theory calculations give further insight into the electronic structures and preferred Li positions in the different structures formed upon cycling, particularly at high lithium contents, where no prior structural data are available. Lastly, the results shed light into the high specific capacity of V 6O 13 and are likely to aid in the development of this material for use as a cathode for secondarymore » lithium batteries.« less

@article{osti_1374427,
title = {Unraveling the Complex Delithiation and Lithiation Mechanisms of the High Capacity Cathode Material V6O13},
author = {Meng, Wei and Pigliapochi, Roberta and Bayley, Paul M. and Pecher, Oliver and Gaultois, Michael W. and Seymour, Ieuan D. and Liang, Han -Pu and Xu, Wenqian and Wiaderek, Kamila M. and Chapman, Karena W. and Grey, Clare P.},
abstractNote = {V6O13 is a promising Li-ion battery cathode material for use in the high temperature oil field environment. The material exhibits a high capacity, and the voltage profile contains several plateaus associated with a series of complex structural transformations, which are not fully understood. The underlying mechanisms are central to understanding and improving the performance of V6O13-based rechargeable batteries. In this study, we present in situ X-ray diffraction data that highlight an asymmetric six-step discharge and five step charge process, due to a phase that is only formed on discharge. The LixV6O13 unit cell expands sequentially in c, b, and a directions during discharge and reversibly contracts back during charge. The process is associated with change of Li ion positions as well as charge ordering in LixV6O13. Density functional theory calculations give further insight into the electronic structures and preferred Li positions in the different structures formed upon cycling, particularly at high lithium contents, where no prior structural data are available. Lastly, the results shed light into the high specific capacity of V6O13 and are likely to aid in the development of this material for use as a cathode for secondary lithium batteries.},
doi = {10.1021/acs.chemmater.7b00428},
journal = {Chemistry of Materials},
number = 13,
volume = 29,
place = {United States},
year = 2017,
month = 6
}

The delithiation mechanisms occurring within the olivine-type class of cathode materials for Li-ion batteries have received considerable attention owing to the good capacity retention at high rates for LiFePO4. A comprehensive mechanistic study of the (de)lithiation reactions that occur when the substituted olivine-type cathode materials LiFexCo1-xPO4 (x = 0, 0.05, 0.125, 0.25, 0.5, 0.75, 0.875, 0.95 and 1) are electrochemically cycled is reported here, using in situ X-ray diffraction (XRD) data. On the first charge, two intermediate phases are observed and identified: Li1-x(Fe3+)x(Co2+)1- xPO4 for 0 < x < 1 (i.e. after oxidation of Fe2+ => Fe3+) and Li2/3FexCo1-xPO4 formore » 0 ≤ x ≤ 0.5 (i.e. the Co-majority materials). For the Fe-rich materials, we study how nonequilibrium, single-phase mechanisms that occur discretely in single particles, as observed for LiFePO4 at high rates, is affected by Co substitution. In the Co-majority materials, a two-phase mechanism with a coherent interface is observed, as was seen in LiCoPO4, and we discuss how it is manifested in the XRD patterns. We then compare the nonequilibrium, single-phase mechanism with the bulk single-phase and the coherent interface two-phase mechanisms. Despite the apparent differences between these mechanisms, we discuss how they are related and interconverted as a function of Fe/Co substitution and the potential implications for the electrochemistry of this system.« less

Combined in situ X-ray diffraction, in situ X-ray absorption spectroscopy, and selected area electron diffraction analyses have confirmed the occurrence of a reversible conversion reaction in the BiF{sub 3}/C nanocomposite upon cycling, which leads to the formation of Bi0 and LiF during lithiation and the reformation of BiF{sub 3} during delithiation. It has been shown that only the high-pressure tysonite phase of BiF{sub 3} reforms during the oxidation sweep and that no bismuth fluoride compound with an oxidation state of the bismuth lower than 3 is formed as intermediate during the lithiation or delithiation reactions. Finally, it has been demonstratedmore » that the different plateaus or pseudo plateaus observed on the lithiation and delithiation voltage profiles stem from polarization changes brought about by the dramatic structural changes occurring in the nanocomposite upon cycling. A model, based on the variation of the electronic and ionic transport mechanisms as a function of the state of completion of the conversion and reconversion reactions, is proposed to explain those polarization changes.« less